import java.util.Scanner;

/**
 * @author gao
 * @date 2025/9/7 12:00
 */

public class Solution {
    public char findTheDifference(String s, String t) {
        int sum = 0;
        for (int i = 0; i < t.length(); i++) {
            sum += t.charAt(i);
        }
        for (int i = 0; i < s.length(); i++) {
            sum -= s.charAt(i);
        }
        return (char) sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            String s = in.nextLine();
            String t = in.nextLine();
            Solution solution = new Solution();
            System.out.println(solution.findTheDifference(s, t));
        }
    }
}